1. Field of the Invention
The present invention relates to washing machines and, more particularly, to a washing machine having a wobbling device which causes a wobbling action of a washboard installed at an inner bottom surface of a spin-drying tub, so as to effectively wash clothes.
2. Description of the Related Art
Generally, washing machines are used to wash clothes by rotating a cylindrical rotary tub containing the clothes and wash water therein. Such washing machines have been typically classified into two types, that is, drum type washing machines and vertical shaft type washing machines. In the drum type washing machines, a rotary tub is horizontally set in a cabinet and is rotated around a horizontal axis of the cabinet in opposite directions. These actions repeatedly move the clothes seated on an inner lower surface of the rotary tub upward, and allow the clothes to be dropped from the top to the bottom inside of the rotary tub, due to gravity, to wash the clothes. The vertical shaft type washing machines are designed such that a rotary tub with a pulsator is vertically set in a cabinet, and is rotated around a vertical axis of the cabinet in opposite directions. The forced water currents generated by the pulsator wash the clothes placed inside the rotary tub of the vertical shaft type washing machines.
The present invention relates to vertical shaft type washing machines. FIG. 1 shows the construction of a conventional vertical shaft type washing machine. The conventional vertical shaft type washing machine comprises a cabinet 1 which forms the external appearance of the washing machine. A tub assembly, consisting of two tubs, is set in the cabinet 1. That is, a washing tub 2 is vertically set in the cabinet 1 and contains wash water therein, while a spin-drying tub 3 is rotatably and concentrically set in the washing tub 2. The spin-drying tub 3 is perforated in its sidewall to have spin-drying perforations 3c. A pulsator 4 is installed on the bottom of the spin-drying tub 3, and generates wash water currents inside the spin-drying tub 3. The vertical shaft type washing machine also has a drive motor 5 and a power transmission unit 6, which are installed in a space between the bottom of the washing tub 2 and the bottom of the cabinet 1. The drive motor 5 is a reversible motor which generates a reversible rotating force. The power transmission unit 6 transmits the reversible rotating force from the drive motor 5 to the tub assembly, thus rotating the spin-drying tub 3 and the pulsator 4.
The top of the cabinet 1 is open to allow a user to place or remove the clothes from the spin-drying tub 3. A door 7 is hinged to an edge of the open top of the cabinet 1. The user is thus allowed to open the top of the cabinet 1 to place or remove the clothes from the spin-drying tub 3. A drain hose 8 extends from the bottom of the washing tub 2 to the outside of the cabinet 1, and discharges the wash water from the washing tub 2 to the outside after a washing mode operation.
The spin-drying tub 3 comprises a bottom part 3a, with a spin-drying shaft holder 9 exteriorly mounted to the bottom part 3a. The power transmission unit 6 has two shafts 6a and 6b. That is, the spin-drying shaft 6a of the power transmission unit 6 is coupled to the bottom of the spin-drying tub 3 by the spin-drying shaft holder 9, while the washing shaft 6b of the power transmission unit 6 passes through the interior of the spin-drying shaft 6a so as to be coupled to the pulsator 4. The pulsator 4 is installed on the bottom of the spin-drying tub 3. The washing shaft 6b rotates the pulsator 4 during the washing mode operation.
The above vertical shaft type washing machine with the pulsator 4 is operated as follows. When the washing machine is turned on, after placing clothes into the spin-drying tub 3, water is primarily fed into the washing tub 2. The reversible drive motor 5 is rotated to generate a rotating force, which is transmitted to the pulsator 4 through the washing shaft 6b of the power transmission unit 6. Accordingly, the pulsator 4 is rotated in opposite directions. Such a reversible rotating action of the pulsator 4 generates forced wash water currents inside the spin-drying tub 3, and the clothes are washed by being forcibly moved along with the forced wash water currents while coming into frictional contact with both an internal surface of the spin-drying tub 3 and with each other.
When such a washing mode operation is completed, after elapse of a predetermined period of time, the wash water is drained from the washing tub 2 to the outside of the washing machine through the drain hose 8 before a rinsing mode operation is started. After the rinsing mode operation, a high speed rotating force of the reversible drive motor 5 is transmitted to the spin-drying tub 3 through the spin-drying shaft 6a of the power transmission unit 6, thus rotating the spin-drying tub 3 in a direction at a high speed to spin-dry the clothes. When a spin-drying mode operation is completed, the washing machine finishes the operation of washing the clothes.
In the washing mode operation of the conventional vertical shaft type washing machine, the pulsator 4 is alternately rotated in opposite directions to generate the forced wash water currents in the spin-drying tub 3, thereby washing the clothes by the forced wash water currents. The clothes are thus forcibly moved in the opposite directions, and are twisted and tangled up to each other. Therefore, the conventional vertical shaft type washing machine abrades and damages the clothes during a washing operation, and forces a user to untwist and untangle the clothes after the washing operation. Accordingly, such a vertical shaft type washing machine is inconvenient to use and promotes rapid wear and tear of the clothes.
In addition, to generate the forced wash water currents, the pulsator 4 must be reversibly rotated in short time intervals during the washing mode operation. Thus, the reversible drive motor 5 consumes a lot of electric power while being repeatedly rotated in the opposite directions at such short time intervals. Such an alternating rotation of the reversible drive motor 5 also reduces the expected life span of the reversible drive motor 5.
Furthermore, the conventional vertical shaft type washing machine with the pulsator 4 is designed such that a desired washing effect is enhanced by forcibly rotating the clothes in the opposite directions using the forced water currents. Accordingly, such a design requires an excessive amount of water in the washing tub 2 during the washing mode operation. A large volume of the water required for the washing operation, in turn, requires an additional use of detergent, inevitably causing a greater harm of the environment. Recent trends show that consumers are making a conscious decision to save water and restrict the use of household chemicals to preserve the environment. Therefore, there is a need to solve the above-mentioned problems experienced by the conventional vertical shaft type washing machines.